Frequency band for the FM radio broadcast in Japan is 76 MHz˜90 MHz, and frequency band for the FM radio broadcast except Japan is 88 MHz˜108 MHz.
For instance, as disclosed in a related art of Japanese Patent Provisional Publication No. 10-13127 (JP10-13127), in a vehicle having a large-sized side glass, a glass antenna to receive FM broadcast wave and AM broadcast wave is provided on the side glass (Patent Document 1).
With respect to the FM broadcast wave, in general, by adjusting a length of the antenna to establish resonance with a frequency band of the FM broadcast wave, a good reception gain can be obtained. With regard to the AM broadcast wave, as shown by a circle drawn by a dotted line which encircles a conductive line in FIGS. 12A and 12B, the conductive line each has a reception effective area for AM wave, and it is generally known that the greater the an area encircled by this circle, the more suitably the AM broadcast wave can be received. For instance, as compared with FIG. 12B in which two reception effective areas of a horizontal part of each conductive line located at a lower side of the side glass overlap with each other, a reception effective area of the glass antenna provided on the side glass for the AM broadcast wave as shown in FIG. 12A in which the two reception effective areas of the horizontal part of each conductive line do not overlap with each other becomes greater.
Regarding the glass antenna for the vehicle disclosed in the Patent Document 1, it is an antenna that can receive both of the FM radio broadcast wave and the AM radio broadcast wave by the fact that a conductive line connecting to a power feeding portion that is disposed at a corner part of the side glass is set to form an S-shape. For the FM broadcast wave, by arranging the conductive line so as to form the S-shape on the side glass, a sufficient length of this antenna to establish resonance with the frequency band of the FM broadcast wave can be obtained. In addition, for the AM broadcast wave, by disposing a part of the S-shaped conductive line so as to extend in the middle of the side glass, the reception effective area of the conductive line of this antenna can be increased.
Further, in this antenna, by connecting an auxiliary line to the S-shaped conductive line and matching an input impedance of the power feeding portion of this antenna with a characteristic impedance of a power feeding line connected to the power feeding portion, the reception gain of the FM broadcast wave can be increased.